This invention relates to a composite magnetic head tip structure for a floppy disc drive apparatus, and to a process for the manufacture thereof.
A conventional composite magnetic head of this kind is shown in FIG. 1, as disclosed in U.S. Pat. No. 4,423,550 and in Japanese Patent Application Publication Nos. 58-182124 and 58-189817.
FIG. 1 shows a composite head tip 1 comprising read-write (R/W) core 2, erase (E) core 3, and molded glass portion 12 which magnetically separates the R/W core and the E core from each other, mechanically joins them, and has a width T of 100 .mu.m. The R/W core comprises an L-shaped side core 4 of ferrite, a center core 5 of ferrite, narrow molded glass portions 10 for controlling or regulating the track width TW on the magnetic medium (not shown), and a gap 8 defined by a non-magnetic layer having a thickness of 1 to 2 .mu.m and composed of a glass layer or a silicon dioxide (SiO.sub.2) sputtered layer. The cores 4 and 5 and the gap 8 cooperate to form a R/W head.
The E core 3 is provided with two tracks defined by gaps 9 and narrow molded glass portions 11 which perform tunnel erasure. The width of the central molded glass portion between the two erase tracks is approximately equal to the width TW of the R/W core.
The process for manufacturing this conventional head is explained below with reference to FIGS. 2-7.
FIG. 2 shows the step where the narrow portions 10 which control the track width of the center core 5 are formed. Ferrite blocks 15 are adhered to a holder 13 at an oblique angle .alpha. (about 10 to 20 degrees). Narrow notches 14 and 14' are formed using diamond bits, and spaced from each other with a predetermined pitch P to obtain the desired track width TW. Glass portions 10 are then molded into the notches 14 and 14' in a high temperature nitrogen furnace, any residual glass is removed as shown in FIG. 3, and the gap facing surface 16 is polished. A non-magnetic gap spacer (not shown) corresponding to the desired gap width is then formed on the surface 16 by sputtering or the like.
The thus formed center core 5 is mated as shown in FIG. 4 with a U-shaped side core 4 prepared in a similar manner, and each track width portion is then precisely aligned and adjusted. Glass welding is performed at edge notches 17 and 18 using glass 19 with a low melting point or the same kind of glass as in the glass portions 10, which mechanically integrates the side and center cores 4 and 5 together.
FIG. 5 shows an E core block 21 formed by a process similar to the process for manufacturing the R/W core block 20. The same pitch P is used as in the R/W core block 20, and the interval D between the two erase tracks is generally equal to the R/W track width TW.
In FIG. 6, the R/W core block 20 is positioned over the E core block 21 at a desired spacing interval D.sub.2 by means of a spacer member (not shown). The center line C.sub.1 of the R/W track is then precisely aligned with the center line C.sub.2 of the two E tracks, whereafter glass is molded into the space between the two core blocks 20 and 21 to form the molded glass portion 12.
The head tip 23 shown in FIG. 7 is obtained by slicing the joined core blocks 20 and 21 along the dotted lines 22 in FIG. 6, and planing down the sides. A further cut or slice along the dotted line 24 in FIG. 7 provides the bulk type of composite head tip 1 shown in FIG. 1.
At the steps of glass welding shown in FIGS. 4, 5 and 6, that is at three separate steps, precise track alignments must be made, which increases the likelihood of track deviations in the final head tips. Moreover, as the R/W gap is separated by 0.4-0.7 mm from the erase gap, the mutual positional control or regulation between the R/W track and the E tracks is very difficult to perform.
At least ten machining steps and four glass molding steps are involved, which complicates the process, reduces productivity and increases cost.